U.S. Pat. No. 8,861,752 discloses a speaker array. The speaker array may include a first speaker cell and a second speaker cell. The first speaker cell includes a first membrane and a first shutter. The second speaker cell includes a second membrane and a second shutter. The first membrane may be configured to oscillate in a first directional path and at a first frequency effective to generate a first ultrasonic acoustic signal. The first shutter may be positioned above the first membrane and configured to modulate the first ultrasonic acoustic signal such that a first audio signal is generated. The second membrane may be configured to oscillate in the first directional path and at a second frequency effective to generate a second ultrasonic acoustic signal. The second shutter may be positioned above the second membrane and configured to modulate the second ultrasonic acoustic signal such that a second audio signal is generated.
FIG. 1 is a cross sectional view of a prior art speaker cell 100. Speaker cell device 100 includes shutter 101, blind 103, membrane 105, substrate 107, controller 109, and spacers 111. Speaker device based on an array of such cells (100) may be a micro electro mechanical system (MEMS) and as small as 3 mm×3 mm. Therefore, speaker device may be suitable for mobile devices because of its compact size.
Substrate 107 can be a silicon substrate of a micro electro mechanical system. Spacers 111 can be configured to separate shutter 101, blind 103, membrane 105, and substrate 107.
Membrane 105 can be electrically coupled to controller 109. Controller 109 can be configured to apply a first signal 115 to membrane 105. In response to first signal 115, membrane 105 can oscillate along a directional path 190 effective to generate ultrasonic acoustic wave 117. Ultrasonic acoustic wave 117 may propagate along the directional path 190 from membrane 105 towards blind 103 and shutter 101.
In some examples, first alternating signal 115 may be a voltage or a current that alternates according to a first frequency. In some other examples, first alternating signal 115 may be some other variety of periodically changing signal such as a current or voltage that may be sinusoidal, pulsed, ramped, triangular, linearly changing, non-linearly changing, or some combination thereof. The oscillation frequency of membrane 105 can be substantially proportional to the frequency of first alternating signal 115. Therefore, by applying different alternating signals 115, controller 109 can control the oscillation frequency of membrane 105.
Blind 103 can be positioned above membrane 105 and below shutter 101. Blind 103 can include a first set of rectangular openings (not shown). Ultrasonic acoustic wave 117 passes through the openings of blind 103 through to shutter 101.
Shutter 101 is electrically coupled to controller 109. Controller 109 can be configured to apply a second signal 113 to shutter 101. In response to second signal 113, shutter 101 can move along a directional path 192 between a first position and a second position. Shutter 101 includes a second set of openings (not shown). The relationship and orientation of the first set of openings relative to the second set of openings will be further described below.
FIG. 2 is a top view of an illustrative embodiment of a prior art speaker array 200. Speaker array 200 can include a first speaker cell device 210 and a second speaker cell device 220. First speaker cell device 210 can include a first shutter 211 and a first membrane 213. First shutter 211 and first membrane 213 are both electrically coupled to controller 230. Controller 230 can be configured to apply a first signal to first shutter 211 and a second signal to first membrane 213. As set forth above, the moving frequency of first shutter 211 and the oscillation frequency of first membrane 213 can be associated with the first signal and the second signal, respectively. A first audio signal can be generated based on the movement of the first shutter 211 and the oscillating membrane 213.
Second speaker cell device 220 can include a second shutter 221 and a second membrane 223. Second shutter 221 and second membrane 223 are both electrically coupled to controller 230. Controller 230 can be configured to apply a third signal to second shutter 221 and a fourth signal to second membrane 223. As set forth above, the moving frequency of second shutter 221 and the oscillation frequency of second membrane 223 are associated with the third signal and the fourth signal, respectively. A second audio signal can be generated based on the movement of the second shutter 221 and the oscillating membrane 223.
When the moving frequencies of first shutter 211 and second shutter 221, and the oscillation frequencies of first membrane 213 and second membrane 223 are substantially the same, the first audio signal can be generated by first speaker cell device 210 and the second audio signal can be generated by second speaker cell device 220 have substantially the same frequency.
When the moving frequencies of first shutter 211 and second shutter 221 are different, or the oscillation frequencies of first membrane 213 and second membrane 223 are different, the first audio signal generated by first speaker cell 210 and the second audio signal generated by second speaker cell 220 have substantially different frequencies.
There is a growing need to reduce the energy consumption of all devices integrated in smartphones/mobile/wearable products, and MEMS speakers.